Apertured electron lens and method of alignment



J. HlLLlER Sept. 8, 1942.

Filed Nov. 15, 1940 J a J 9 Z Bnventor Gttorneg Patented Sept. 8, 1942 APERTURED ELECTRON LENS AND METHO OF ALIGNMENT James Hillier, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application November 15, 1940, Serial N 0. 365,773

3 Claims.

This invention relates to an apertured electron lens and particularly to the method of aligning the aperture and the lens.

Some electron lenses are provided with diaphragms which include a minute aperture. If distortion is to be avoided, the aperture must be aligned with the axis of the lens. In the lenses of the prior art, the alignment of the aperture has been most difiicult; often alignment has been accompished by cut and try methods after the lens had been assembled in an electron microscope or the like.

It is an object of the invention to provide an apertured lens with means for aligning the aperture on the axis of the lens. Another object is to provide a simple effective method for aligning an electron lens and an apertured diaphragm. A further object is to provide an improved objective lens including magnetic pole pieces and means for centering an apertured diaphragm therein,

The invention will be described by referring to the accompanying drawing, in which Figure 1 is a sectional view of one embodiment of the invention; Figure 2 is a view of the pole pieces in section, and the light source and microscope illustrating the method of alignment; Fig. 2a is an enlarged sectional View of a portion of Fig. 2; and Figures 3 and 3a illustrate, respectively, the images of an improperly and a properly aligned aperture. Similar reference characters will be applied to similar elements.

Referring to Fig. 1, pole pieces I, 3 which are held together by a suitabletubular member 5 are mounted within a magnetic structure T. The magnetic structure includes a magnetic shell 9 and a magnet winding II. The pole pieces are machined to insure concentricty of all of the parts and especially the conical portion l3 and the portions of the pole piece adjacent the tubular member 5. An adjustable centering piece I5, hereinafter described in detail, is screwed into the lower portion of the pole piece. The centering piece includes the apertured diaphragm l'l.

Referring to Fig. 2, the centering piece l5 includes an outer tubular member 19. On the upper end of the outer tubular member are arranged adjusting screws 2I which engage an inner tubular member 23. On the lower end of the outer tubular member is secured a flexible diphragm 25. The flexible diaphragm carries the inner tubular member 23 and acts as the fulcrum for the centering adjustments. The diaphragm I! which includes the minute aperture 21 is demountably located on the lower end of the inner tubular member 23 by means of an insert member 3| and a cap member 33. Since the apertured diaphragm is demountable, it may be readily removed for cleaning or replacement.

The pole pieces, including the centering member [5 are mounted on a hollow frusto-conical bearing 35. The bearing surface is machined to fit as perfectly as possible the conical surface 13 of the pole piece I. A light source 31 is located above the axis of the center-member l5 and a microscope 39, which may include a mirror 4|, is arranged to receive the light image of the aperture 21.

The method of aligning the aperture is as follows: The pole pieces are rotated about the conical bearing 35. If the aperture is improperly aligned with respect to the axis of rotation, and therefore the axis of the pole pieces, the light image 43 will rotate about a center 45 as shown in Fig. 3. The observer adjusts the screws 2| so that the image moves toward the center. The pole pieces are again rotated and the image should rotate about but near and perhaps on the center. When exact alignment has been obtained, the aperture will rotate about its own center as illustrated by Fig. 3a. After proper alignment has been obtained, the pole pieces, including the centering member l5, are inserted within the magnetic structure 1 as shown in Fig. 1.

Thus, the invention has been described as an apertured electron lens. The apertured member is a minute hole in a diaphragm which is mounted on the end of a center member. The center member is arranged so that the diaphragm may be moved radially with respect to the axis of the lens. While the invention has been described by referring to a specific form of magnetic lens, the invention is not so limited. The method of adjusting the apertured diaphragm may be practiced with any type of electron lens and is not limited as to the shape of the pole pieces, demountable nature of the diaphragm, fulcrum of the centering device and the like. For example, the diaphragm need not be demountable; the fulcrum may be a ball and socket joint; the adjusting device might be an eccentric ring; and the bearing cone 35 might be formed in any desired manner.

I claim as my invention:

1. An electron lens including pole pieces, an outer tubular member secured coaxially with respect to one of said pole pieces, an inner tubular member adjustably mounted within said outer member, an apertured diaphragm mounted on said inner member and movable therewith into axial alignment with said pole pieces, and means for adjusting said inner tubular member with respect to said outer tubular member and with respect to the axis of said pole pieces.

2. A pole piece assembly for an electron lens including a pair of pole pieces having a common axis, a hollow centering member secured substantially coaxially to one of said pole pieces, a hollow adjustable member substantially coaxially and adjustably mounted within said hollow centering member, an apertured diaphragm mounted on said hollow adjustable member, and means for moving said hollow adjustable member so that said diaphragm and its aperture may be aligned with the axis of said pole pieces.

3. A pole piece assembly for an electron lens including a pair of pole pieces having a common axis, a hollow centering member secured substantially coaxially to one of said pole pieces, an inner hollow member located within said hollow centering member, a flexible diaphragm jointing said members, an apertured diaphragm mounted on said inner hollow member, and means for adjusting said inner member so that said aperture may be aligned with said common axis.

JAMES HILLIER. 

